Heart failure is a leading cause of hospitalization in patients older than 65 years old and continues to be associated with high mortality rates. For example, 30 to 40 percent of patients with advanced disease and 5 to 10 percent of patients with mild symptoms die within five to 10 years. Presently, approximately 5 million people in the United States experience heart failure (HF) along with 500,000 newly diagnosed cases per year.
Effective HF therapy can depend upon early detection of lusitropy or diastolic dysfunction). Lusitropy is typically determined through imaging techniques such as echocardiography. Echocardiography is prone to interpretation error depending on the experience of the sonographer. Although nuclear imaging techniques have addressed some of the limitations with echocardiography, echocardiography remains the basic technique to measure diastolic dysfunction.
Another method for determining diastolic dysfunction is presented in U.S. Patent Application Publication 2007/0100249 (now U.S. Pat. No. 7,959,576) to Torpo et al., published May 3, 2007, and entitled Apparatus for Detecting Diastolic Heart Failure. Torpo et al, detetunnes the presence of diastolic heart failure by extracting time duration data during diastole from a sensed IEGM signal. In particular, Torpo relates to using isovolumic relaxation time (IVRT) to detect diastolic heart failure. IVRT occurs during a “still” period or when the heart relaxes without changing volume. In particular, IVRT occurs during the time from the closing of the aortic valve to the opening of the mitralis valve. IVRT is determined from impedance measurements between the left and right ventricles, or between the left ventricle and right atrium. One disadvantage to the method used in Torpo involves determining diastolic heart failure during a pseudonormal state. Torpo et al, may fail to detect a pseudonormal state since the IVRT of a pseudonormal state is about the same as a IVRT for a normal state, as shown, for example in FIG. 1 of Torpo et al. Additionally, Torpo fails to use the LV accelerator signal which provides accurate data as to relaxation abnormalities. It is therefore desirable to determine the presence of relaxation abnormalities in a patient without the limitations associated with the conventional methods used.